Controller for magnetic induction accelerators



Dec. 26, 1950 w. F. WESTENDORP 2,535,710

CONTROLLER FOR MAGNETIC INDUCTION ACCELERATORS Filed Sept. 25, 1946 3 Sheets-Sheet 1 Fig.1.

lnventoT: Willem F. Westendorp, y W

His Attovneg.

1950 w. F. WESTENDORP 2,535,710

CONTROLLERFOR MAGNETIC INDUCTION ACCELERATORS Filed Sept. 25, 1946 r s Sheets-Sheet 2 Fig.5.

INJECTION TIM/N6 C/RC 1 1/ T Inventor: Willem F. Westendorp,

His Attorneg.

Dec. 26, 1950 w. F. WESTENDORP 2,535,710

CONTROLLER FOR MAGNETIC INDUCTION ACCELERATORS Filed Sept. 25, 1946 3 Sheets-Sheet 5 Fig.7. Vcl

Fig.8.

000000 Ouu Inventor: Willem F Westendorp,

His Attorneg.

Patented Dec. 26, 1950 CONTROLLER FOR MAGNETIC INDUCTION ACCELERATORS Willem F. Westendorp, Schenectady, N. Y., as-j signor to General Electric Company, a corporation of New york ApplicationSeptember 25, 1946, Serial No. 699,284

The present invention relates to apparatus for imparting highenergy to charged particles, in particular electrons, by means of magnetic induction effects. The invention i especially ap plicable in connection with apparatus of the type disclosed in my prior Patent 2,394,071, granted February 5, 1946, to the General Electric Conrpany, a corporation offNw York.

Apparatus of the character referred to includes a closed vessel and a magnetic system for producing a tirne varying magneticfield which so links the intended orbit of the particles desired to be affected by the apparatus as to induce'a field adapted to accelerate the particles in such orbit. A further magnetic field varying concurrently with the accelerating fieldiscreated at the locus of the accelerating orbit with such space distribution as to balance the centrifugal tendencies of the particles and to maintain themin the preferred orbit. I p

It is found that concurrent and conforming variation of the accelerating and restraining fields results in a stable orbit of the accelerated particles as long as the particles remain at low or moderate energy levels. However, as the energy'of the particles increases with continuing acceleration, their rate of energy loss due to radiation mounts non-linearly in a. manner which progressively destroys the orbital balance and.tends to produce deviation of the particles from their desired path before'the highest energy levels areattained. This effect hasheretofore been considered'to impose a limit upon the-energy levels attainable by apparatus of the type in question. 1 U

' It is an object of the present invention to provide means by which the orbit destroying effects attributable to radiation losses may be overcome to a degree which will materially extend the effectiveness of magnetic induction accelerators. In one aspect, the invention includes the provision of means for causing the rate of change of the accelerating field to exceed that of the orbit-restraining field as the accelerated particles approach high energy levels so that the loss of energy by radiation is effectively offset. From another viewpoint, it comprises the provision of an arrangement by which the accelerating and guide fields can be varied concurrently and at the same rate of change throughout a portion of I the operating cycle and thereafter causedto vary at different rates throughout the remainder of the cycle. i The features of theinvention which I desire to protect hereinare pointed out with particularity 9- Claims. (Cl. 250'27) in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following pecification taken in connection with the accompanying drawings in which Fig. 1 is a partially sectionalized elevation of an accel'jerator suitably embodying the invention; Fig. 2 is a fragmentary view, partially broken away. which shows in detail some of the features of the discharge vessel of Fig. 1'; Fig. 3 is a graphical representation useful in explaining the invention; Fig. 4 is a diagrammatic circuit illustrating in fundamental form one aspect of the-invention; Fig.5 is a further graphical representation; Fig". 6 is a more elaborate circuit diagram which i1:- lustrates in detail certain of the features of the invention; Fig. 7" is a further graphical representation explanatory of-the operation of Fig. 6; Fig. 8 illustrates an alternative mode of application of the invention, shown schematicalIyYand Fig. 9 is a graphical representation used in explaining Fig. 8. I

3 Referring particularly to Fig. 1, thereis shown in section a closed annular glass vessel- Ill. The space within the vessel provides a circular orbit ii -which charged particles, specifically electrons may be accelerated tohigh energy levels The vessel is preferably highly evacuated and. a high resistance coating, such as an extremely thin layer of silver (not shown) is applied to the inner surface of thewall to prevent wall-charg ing. Within'the vesseldflthere is provided a thermionic cathode 40 (see Fig. 2) which inconnection with associated electrodes 4| and 4 2 serves as asource of electrons to be accelerated. The electrodes -42 are supported by a stem 43 and are supplied with energizing potentials by lead-in wires 44 sealed into the'stem.

The accelerating mechanism comprise a mag;- netic structure including an outer rectangular frame H of laminated magnetic material. Bridging the upper and lower parts of the mag;- netic frame at its central region, there is pro;- vided a circula core l2 which provides a flu; path concentric with the vessel in asviewed from above. Annular pole pieces l3 and I 4 which have a low reluctance connection l5 with the core 12 are arranged above and below the-vessel it so as to produce a concentration of-fiux through the vessel at the locus of the desired orbit of electronsto be accelerated within the vessel. There are provided coils IT and H8 which surround the pole pieces. I3 and M and which primarily control the passage of flux through these pole pieces, and there is further provided a coil 20 which surrounds the core 12 and primarily controls the flux through it.

As will be further explained at a later point, means are provided for energizing the coils l8, and 2! to vary the magnetization of the core system above described in a generally sinusoidal fashion. Electrons produced, within the dis charge vessel are affected in two ways by the variations in magnetic flux thus obtained. In the first place, since the magnetic flux traversing the core l2 links the circula :path provided by the vessel, any variations of such flux necessarily produces an electric field tending to accelerate electrons projected along such path. .In this latter respect the apparatus is comparable to a transformer with a secondary comprising a circular path along which the various electrons are accelerated. In general, although the voltage per turn in such a transformer may be low, within a practically attainable range of flux variation the electrons can be made to achieve Very high energies (several million electron volts) be- .cause of the tremendous number of turns which they may execute during a single cycle of magnetic fiux variation. In addition to the acceleration produced by flux linking the electron path, the flux produced by the annular pole pieces l3 and M in the region (locus) of the electron orbit tends to cause the electrons to follow an inwardly spiraling path. .It has been shown that by a proper design of the magnetic structure the centripetal force produced by the magnetic field existing at the electron orbit may be caused to bal ance the centrifugal tendencies of the accelerated electrons. .In general, this result requires that the following relationship be satisfied:

Where A175 is the total change in flux included in the electron orbit, v isthe radius of the orbit and Br is the flux density at the orbit. This is referred to as the 2: 1 flux relationship. It is readily practicable to design the magnetic structure in such a fashion as to eilect the balanced relation of guide field and enclosed flux which is desired for the purpose specified above and which is further necessary for radial and axial stability of the electron orbit. The principles governing the proper space distribution of the guide flux are more fully set forth in DJW. Kerst U. S. patent application Serial No. 445,465, filed June 2, 1942, and assigned to the General Electric Com" pany, a corporation of New York, now matured into U. S. Patent No. 2,394,070.

When all the conditions specified in the fcregoing are fulfilled. electrons introduced into the chamber ii! in a period when the magnetic field is increasing may be expected to be drawn into the particular orbit in which a balance of centripeta'l and centrifugal forces exist and to be continuously accelerated along such orbit as long as the magnetic field increases in value. 'By this mechanism, electrons may be brought to energylevels on the order of several million elec- "tron volts with a continuous balance being main- 'tained between the increasing centrifugal forces operating on the accelerated electrons and the increasing centripetal forces maintained b the constantly increasing magnetic gu'ide field. However, as the higher energy levels are approached, another factor comes into play in that the rate of 'energyloss of the electrons attributable to electromagneticradiation tends toincrease to a point .at which .it becomes a significant factor in the equations of motion of the electrons. The result is, therefore, that the orbital stability initially accomplished by the concurrent growth of the ac celerating and guide fields can no longer be maintained and the electrons tend to spiral inwardly toward a point at which they will be intercepted by the structure of the discharge vessel or of the electrode elements within it. Because of this circumstance, it has been suggested that an up per limit is imposed upon the field of usefulness of magnetic induction accelerators. In accordance with present invention, however, this eirect can be overcome in a manner which will now be described.

Several writers have derived substantially the same expression for the energy loss of electrons moving in a circular path in a magnetic field, viz. 5.44% iii- B watts per electron, where B is the magnetic field strength, and R the radius of electron gyration, both expressed in M. K. S. units.

.At the energy levels at which radiation losses become material to the operation of magnetic induction acceleration, the electrons maybe considered to have attained substantially the velocity of light, designated by the constant c. We, therefore, may write the time for one revolution of a given electron as Combining this expression with the expression given above for "radiation energy loss and recognizing watts per electron as being equivalent to joules per second per electron, we may express the loss per electron-as sai-x'i'oe eegl joules/revolution But electronic energy measured in joules is also expressible as e-V where e is the electronic charge in M. K. S. units and V is the accelerating otentied in volts. We may, theretore, say that the energy loss per revolution attributable to radiation is equivalent to a decrease in accelerating voltage determined by the following equation:

Substituting the lmovmvalues of the various con" stants, we have V (10ss per revolution) 712B R (in M- K. S. units) This interpretation of the nature of the losses attributable to radiation at high energy levels ofiers the possibility of oilsetin such losses by introducing into the accelerating system a corrective voltage Vs which increases at a rate corresponding to the rate of increase of the loss function. In Fig. 3 the introduction of such a corrective voltage is indicated by superimposing on the normal sinusoidal accelerating flux m produced through the central core 12 of the ac- =celerator-of Fig. 1 a corrective "fluxes adapted to produce a :corrective accelerating voltage of the desired magnitude. Ehe production of this cor 'rective flux assumes the induction the coil by which the flux is produced of a corrective voltage "V0 which is shown as being superimposed upon the normal voltage function Vn. .My invention is concerned in large part with the provision of means .for suitably applying the corrective voltage Vs.

Any attempt to employ the foregoing analysis in overcoming the d fficulties attributable to radiation losses requires consideration of the fact that the increased-rate of growth of the accelerating V- (in S. units) flux, which appears to be required as high energy levels are approached, must be an increase relative to the rate of growth of the guide flux. That is to say, enhancement of the accelerating flux must occur without a corresponding enhancement of the guide flux in order that the forcestending to produce outward motion of the accelerated electrons may not be offset by a corresponding increase in the strength of the centripetal force exerted by the guide field. This presupposes, therefore, that the strengths of the accelerating and guide fields may be independently controlled while maintaining them wholly synchronized and coordinated as far as their normal rate of growth is concerned.

An approximation to the ideal form jof radiation compensation visualized in Fig. 3 may be produced on a basis consistent with the foregoing requirement by a circuit arrangement such as that shown in Fig. 4. In this circuit the coils l1, l8 correspond to the correspondingly numbered guide field coils of Fig. l, and the coil 20 corresponds to the accelerating coil of Fig. l. The coils are connected in a parallel resonant circuit which includes coils H, i 8 in one of its branches and the coil 2!! in series with a capacitor 30in its other branch. Power is supplied to the various coils by means of a, transformer having a multiterminal secondary winding 32 and a primary winding 33 which is assumed to be connected to a suitable power source such as a 60 cycle supply (not shown). The common point of the coils l1, l8 and of the capacitor 30 is connected to a terminal 35 of the transformer winding 32, which terminal is indicated as being variable for purposes of permitting adjustment of the electron orbit as controlled by the potential applied to the coils I1, l8. A second transformer terminal 31 is connected to the common point 38 of the coils l1, l8 and the coil 20 through an electronic circuit including controlled gaseous discharge tubes Q5 and 46 the function of which will shortly be described. A third transformer terminal 48 intermediate in potential between the terminals 35 and 31 connects to the common point 49 of the coil 2|] and the. capacitor 30.

} Assuming the discharge devices 45, 46 to establish an effective conductive connection between the terminal 3'! and the point 38, as they will later be shown to do, the characteristics of the circuit described are such that the relationship between the guide field produced by the coils l I, l 8 and the accelerating flux produced by the .coil 2|! may be definitely fixed by properly selecting the ratio of turns of the transformer sections 35-48 and 48--31 to produce the aforementioned 2:1 flux relationship. For present purposes the two guide coils have together substantially the same number of turns as the accelerating coil and are connected in bucking relation with it in series with the capacitor 30. By excitation derived from the supply transformer 32, sinusodial oscillatory currents are set up in the series circuit consisting of'the accelerating coil 20, the guide coils l1, l8 and the capacitor 30. Since thepole pieces l3 and M of Fig. 1 are encircled only-by the coils l1 and I8, the flow of currents in,,thQSe coils will establish a guide flux between the. pole pieces. However, since the central core I links both the coils I I, I8 and the coil 20 and since these coils are in bucking arrangement, no flux will be produced in the core by the oscillatbri'burrents re ferred to. Conversely, any fiuxnproduced in the core l2 by a voltage separately applied to the terminals of the coil 20 will induce an equal and opposite potential in the coils I1 and I3 and will thus prevent current flow in such coils attributable to the application of such voltage. Accordingly, voltage separately applied to the coil. 20 will affect the accelerating flux in the core l2 without modifying the guide flux produced between the pole pieces I3 and M by the coils l1, l8. Means for applying such a voltage in a way which will maintain the desired 2:1 flux relationship above referred to and at the same time produce an accelerating flux calculated to offset energy losses attributable to radiation are described in the following.

It is hardly practical (although not theoretically impossible) to produce through the central core l2 a compensating flux in exact accordance with the time function indicated by the shaded area of Fig. 3. However, an adequate approximation can be obtained by means of the circuit elements shown at the upper right-hand corner of Fig. 4. Specifically,'there is illustrated a con trolled gaseous discharge tube which is connected between the resonant circuit point 38 and a terminal 56 of the transformer winding 32 which is relatively higher in potential with respect to terminals 35 and 48 than is the terminal 31. The control element 58 of the discharge tube 55 is assumed to be so energized as to render the tube conductive at a point in the operating cycle of the apparatus as awhole at which radiation losses have become significant. Assuming a lag-- ging current to be flowing at this time from the transformer 32 through the tube 46 and into the coil 20 (as will be the case in the normal operation of the equipment), the act of rendering the tube 55 conductive will cause current flow to com mutate to that tube (i. e., by causing cessation of conduction in tube 46) with the result that an increased voltage will immediately be impressed across coil 28. The magnitude of this increase will be that of the potential difference between the terminals 31 and 5B and may be made of any value considered necessary to produce the desired radiation compensation. Because of the bucking arrangement of the accelerating and guide coils described above, the increase in the flux produced by coil 2|] will develop in the coils l1 and [8 an induced voltage equal and opposite to the increase in the total voltage applied between the circuit points 38 and 49 so that no change in guide field flux will occur. It can be proven that for the attainment of this ideal condition the coils l1, l8 should aggregate slightly more turns than the coil 20; this being attributable to the finite reluctance of the return magnetic path through the yokes and legs of the magnetic frame I I. If zero reluctance of this path could be realized, an equal number of turns in the guide coils and accelerating coils would be indicated.

The effect of the operation of the circuit arrangement just described is illustrated graphically in Fig. 5, which is to be compared with the ideal conditions assumed in Fig. 3. As will be seen, the functioning of the discharge tube 55 at a time t1 imposes uponthe voltages V11 normally applied to the accelerating coils 20 a pulse of cor rective voltage Vc which may initially be in ex, cess of the ideal value but which in time assumes a level below the ideal value, the average result being not far from that considered ideally desirable. In terms of fluig change, the effect of the operation of the discharge tube 55 is represented by the shaded area {be superimposed upon the normal flux curve c511,.

While the result obtained in accordance with Fig. may seem an unduly coarse approximation of that indicated as desirable in Fig. 3, a relatively large tolerance is permissible in view of the fact that the electron energy is determined not by the instantaneous voltage per turn but by its integral from the moment of injection, that is to say, by the flux within the orbit. If the total flux encircled at a particular moment is a few percent lower than what it should be in order to maintain the proper orbit diameter, the orbit diameter will shrink by an approxi- .mately coresponding percentage, but unless a relatively large departure is involved, this will not result in interception of the electrons.

Fig. 6 illustrates in somewhat more complete detail circuit arrangements by which results of the character outlined in the foregoing are obtained. In this figure, elements corresponding to iterrs previously described in connection with l and 4 bear identical numerals. In accordance with the arrangement previously outlined, a transformer having a secondary winding supplies energy to a resonant circuit comprising an accelerating coil 28, guide coils l1, l8 and a capacitor 3%. An annular discharge vessel iii is provided in such relation to the magnetic structure served by the coils (see Fig. 1)

to permit electrons released within the ves- .sel to be accelerated to high energy levels in a circular appropriate point in the operating cycle is accomplished by means of a winding 5! inductively coupled to the coil 1'! and connected to the accelerating electrodes (not shown) of the device is through a timing circuit indicated diagrammatically by the block outline 62. The winding Eli and the timing circuit 52 are preferably of the character described in my prior Patent -2,39' .-.,t '7l previously referred to herein. The coil 2% is connected to terminal 31 of the trans former winding 32 through a circuit which includes controlled gaseous discharge devices 35 and connected in back-to-back relationship so as to be conductive during predetermined portions of the opposite halves of the operating cycle. Additional tubes and 55 provide means for alternatively connecting coil 29 to transformer terminals 5% and El in accordance with a mode of operation to be explained in the following.

The operation of the circuit so far described may best be understood by reference to the graphical representations of Fig. 7 in which the upper curve V may be taken to represent the voltage appearing across the coil 2b of the accelerating apparatus. The curve I represents the magnetizing current through the 'coil 2!] as supplied through the transformer winding 32, and the curve c represents the flux which links the electron orbit within the vessel H as the result of current flowing in the coil 20. The displacement between the curves of current and flux is explainable as the result of losses occurring in the magnetizing circuit.

In order that the tubes (i5, 45, 55 and 65 may each be rendered conductive at the points in the operating cycle of the apparatus, they are respectively connected through appropriate circuits to an auxiliary transformer winding inductively coupled to the winding 32 (e. a winding upon the same transformer core). This connection assures synchronization between the grid control of the various-tubes and the alternations of the exciting current supplied to the various coils of the accelerating apparatus. In the case of the tube 46, connection orbit. Injection of electrons at anv desired of its grid 45' to the auxiliary supply source 89 is through a coupling transformer H connected in such fashion-that the tube 45 is automatically rendered conductive during the positive portion of the cycle,- thus permitting currentof-the indicated polarity to flow to the coils during his portion of the cycle. The tube 45, on the other hand, has its grid ie" reversely connected through a transformer 12 so that it is automatically conductive during the negative portion or" the voltage wave. The electron injecting circuit provided by the combination of the winding and of the timing circuit 62 is so adjusted as to-cause electrons to be injected into the discharge vessel it at or nearthe point 751 at which the flux wave 5 (Fig. 7) passes through zero value. Accordingly, acceleration of the electrons thus induced occurs as the flux continues to increase-due to continued flow of current through the exciting coils.

- The flux continues to increase along a sinusoidal curve until a time is at which it is assumed that the effect at the electron orbit of e gy losses attributable to radiation is beginnin to become significant. A this point it is desired to render the tube abruptly conductive so that the voltage applied to the coil 20 may he suddenly increased by connecting the coil through the tube to the transformer terminal To accomplish this result, there is provided in connection with the grid 55' of the tube 55 a timing circuit connected between the grid and the auxiliaryvoltage source 59. cuit incluues a conventional phase shifting network including a reactor 755 having serially connected across it a resistor it and a capacitor 11. Terminals it and it are respectively provided at the midpoint of the reactor iii and at the junction point of the resistor and the capacitor II, the phase of the voltage between these terminals being determined by the relative impedancevalues of the resistor and the capacitor in accordance with principles well understood in the art. For present purposes,,the adjustment is such as to produce a lag on the order of 60 between the voltage of the source 39 and that appearing at the terminals. '58 and I9. vThis phase-retarded voltage is applied to the primary of a peaking transformer 82 having its secondary connected directly in the grid circuit of the tube A biasing battery 55 connected in this grid circuit assures that the tube 55 shall not become conductive until a pulse of peaked voltage is delivered by the transformer 82 in accordance with its peaking characteristics.

Upon application of a voltage pulse to the grid 55 of the tube 55 through attainment of the proper level of the voltage applied to the transformer 82, the tube becomes conductive, thus establishing a circuit between the coil 2e and the transformer terminal The voltage then existing across the parallel circuit including the tube .45 can be shown to be in such dir ction as'to cause extinction of thistube with resultant commutation of the current to the coil to the tube 55. This operationwlaich is assumed to occur at the time is (Fig. '7), results inan abrupt increase in the voltage appliedto th coil 20, as indicated at Va A corresponding increase I6] will be occasioned in magnetic t current and this in turn willlead to enhancement (is, of the flux produced in the central core of the magnetizing structure.

In order more closely to approximat the ideal waveform ,of the compensating flux required to offset radiation losses (as indicated, for example, in Fig. 3)., a second enhancement of the flux is accomplished at a slightly later time by the action of the tube 65. Like the tube 55, this tube is controlled by the action of a phase shifting circuit which, in this case, includes a reactor 90 and the series combination of a resistor 9| and a capacitor 92. Terminals 93 and 94 are provided in connection with this network from which a voltage is derived for application to a peaking transformer 96 which is connected to the grid 65 of the tube 65. A battery 91 connected in circuit with the grid 65 assures that the tube 65 shall not be rendered conductive until a favorable voltage pulse is delivered by the transformer 96. The adjustment of the impedance values of the phase shifting network 90, 9|,92 is such as to cause the tube 65 to be triggered at a time t: (Fig. 7) which follows by a definite interval the triggering of the tube 55.

-. At the time is the tube 65 functions to establish a conductive connection between the coil 20 and the transformer terminal 61, resulting in a fur ther voltage increase Ve in the potential applied to the coil 20. This results in a change I in the current flowing in the coil which in turn augments the accelerating flux by an amount e It is to be noted that current flow is commutated from the tube 55 to the tube 65 in accordance, with a mode of operation previously explained. If desired, a ballast circuit including a resistor 99 and a condenser I60 may be placed in circuit with the tube 65 as shown so as to limit the current drawn from the transformer 32. The con denser I00 has the further function of assisting commutation of current control back to the tubes 45' and 46 as the voltage V (Fig. 7) passes through zero. As has been previously explained, the tube 45 is connected so as to become conductive at the time of voltage reversal.

Th functioning of the apparatus described in the foregoing results at the appropriate point in the operating cycle in an increase in the accelerating flux (i. e., the flux through the core I2) as contrasted with the guide flux produced at the locus of the electron orbit. This in turn prevents the inward spiraling of electrons which would otherwise result because of energy losses attributable to radiation and in effect maintains the electrons in a stable orbit for a longer ac-' celerating period than would otherwise be realized. This permits the ,total energy of theelectrons to be brought to a higher level than Ultimate diversion of the electrons may be accomplished by the provision of pulse operated orbit shifting means of the character described inG. C. Baldwin Patent 2,331,788, granted October 12, 1943, or alternatively of the character described in my prior Patent 2,394,072, granted February 5, 1946. material part of my present invention, it does not require to be descrlbedin detail herein. Very generally, however, it may include auxiliary coils for superimposing an orbitdiverting field upon the main field of the magnetic structure, together with appropriate circuits forabruptly energizing such auxiliary coils at a desired point in the accelerating cycle. v diverting means, the diverted electrons may be intercepted by a target (not shown) appropriately provided in the discharge vessel, or other means may be employed to assure that the accelerated Since such means forms no Upon operation of the orbit can beusefully employed outside the discharge vessel. c

In a preferred embodiment the invention may be usefully combined with D.-C. biasing provisions of the type described and claimed in my prior application Serial No. 616,634, filed September 15, 1945, and assigned to the same assignee, as the present application. An arrangement serve ing this purpose is illustrated in Fig. 8. In this figure only the magnetizing circuits are shown, it being assumed that the accelerating vessel and the magnetic structure areidentical withthose described in connection with Fig. 1.

In Fig. 8 there are shown guide field coils III] and |II connected in bucking relation to an accelerating coil II2 which with acapacitor II3, completes. a parallel resonant circuit. The excite ing circuit for the resonant system includesa transformer having a primary or input winding H5 vand a secondary winding II6 which is provided with a number of appropriately displaced terminals II! to I2I, inclusive. The potential occurring between the terminals Ill andIIB connected to the resonant circuit capacitor II 3 through a blocking capacitor I25, the function of which will-shortly appear. The terminal II! in-.

volves an adjustable tap arrangement which can be used to fix the relationship between the total;

excitation of the coils IIU, III and the coil II2 so as properly to locate and stabilize the orbit of the electrons desired to be accelerated. The coil;

H2 connects at one end to the transformer terminal IIBthrough the blocking capacitor I25 and at its other end may be variously connected to the terminals III9, -It'll and I2! through con trollable discharge tubes :21 to I30. The buck ing connection of the coil H2 with respect to the} coils Ill] and III means that changes in the potential applied to the coil II2 will be reflected.

sioned by a change in voltage across coil IIZ. Ac cordingly, increasing the potential applied to the coil II2 by sequential energization of the tubes I I28 to I30 in the order'specified will permitan increase in the relative magnitude of the ac., celerating flux to be effected in accordance with principles previously described herein. This will. ofiset the effects of losses attributable to radia.-.l tion as the accelerated electrons. approach high.

energy levels.

As has been shown in my prior applicationf Serial No. 616,634, above referred to, the power losses in a magnetic accelerator of given dimensions may be appreciably reduced and the oper ating range of the accelerator correspondingly extended by superimposing upon the alternating,

guide field a unidirectional field of appropriate value at point X2 is obviously materially greater than that realizabl between 2%, the point of reversal in the absence of bias, and X2. In effect...

It will be noted -that Aqi remains positive. provided c is changing along a curv'e' of positive slope even-' though the flux is negative at. the instant from:

which mpis measured.- This suggests that as far as the accelerating fillX is concerned the use: of a unidirectional component; to assure a longer periods. of positive flilX is unnecessary; Moreover; i'ti's definitely undesirable because it may cause premature saturation of the magnetic core when added to the alternating flux. viewpoint, the use of a unidirectional flux: com-- ponent throughthe core which passes the accelerating flux may'requirethe core to: be larger than would otherwise be necessary in order to avoid premature saturation.

It is found that in=connection with a: structural arrangement" such as that of F-ig'. 1', the obje'ctive of producing a unidirectional flux component in theguide-fieldarea Without concurrently produc i'n'g such ac'omponent through the central" mag netic' core may be accomplished by the arrangements indicated in Fig. 8: Asillustrated; a source of D.-C. potential [35 isconnectedin par aliel circuit with the resonant circuit" capacitor I i-3 a choke reactor l36 bein'g connected in series with the D961- source" in order to prevent un wanted A'.-C currents from flowing through the latter; A- capacitor 31 which shunts" the D.-C source I35 permits the fiow of the necessarymagnetizing current for the reactor [36 without requiring that such current pass through the DE-C. supply source. The blocking condenser r25, previously referredto, revents D.-C'; cur rent from reaching" the transformer" H6.

As aresult of the bushing connection of coil= H2 with respect to the coils I if) and Hi, the" Dz-C. current flowing through these coils is es-- sentially" self -neutra-lizing' as far as its magnetic ing eii'ec't upon the central core of the magnetic structure is concerned. Thatis t'osay, the mag netizing effect in one direction attributable to the coil H2 is offset by the" equal magnetizing efiect in the other direction of the coils Hi1" and HI.

This is not the case, however, with respect to" flux produced in the guide-field region, which is outside the coil H2 (see the" construction of Fig. 1"). The effect of the DE-C. current flowing in the coils H0 and III is, therefore, not neutralizedas far as the guide field is concerned and the d esired unidirectional biasing" of this guide field in accordance with the graphical representation of Fig. 9 is obtained. The net result, therefore, is thatt'he advantages in terms of decreased power requirements and diminished size of equipment attributable to this feature areusefuli'y combinedwith the means previously described for com pen'sating radiation losses.

It can be shown that for the ideal condition of zero" unidirectional iiux' through the centr a1 core;

iii

f2 the guide coils II BT and: HI. should: aggregate slightly more turns than the coil H2, this being. caused by differences in the magnetic paths in-- volv'ed with respect to the: two coils. With exactly this' same: turnratio, any rate of change" oi fiuxpresent-in the central core will produce equalvoltages in the two sets ofcoils, thus assuring: the desired absence of anyreaction: upon. the guide field ofthe compensatingflux producedv from time totime through altering'the energiza tion of the coil H2 Disturbance of the electron orbit may be; ac-' complished when: the desired degree oil electron acceleration has been attained by pulse-operated orbit-shifting means ofthe type previously referred" to herein.

While the" means described in the foregoing for introducingcompensating voltages to offset radiation losses donot realize the ideal curveof compensation as illustrated, for example,- in Fig; 3', the closeness of the: aproximati'on can be materially improved" by increasing the number of voltage steps included inthe compensatin circuit; Alternatively, it is entirely possible by means of electronic circuits of refined design" (well within the presentv knowledge of the: elec-= tron-ics art) to provide in. a separate source a compensating voltage having a wave form corre sponding precisely to the ideal wave shape; Asa practical matter; however; the arrangements shown herein represent at suflicient improvementover what can be' realized: in the absence: of compensation to be considered adequate for all practical purposes: and to obviate: the need for a more elaborate approach.

What- I claim as: new. and desire to se'c'ureby Letters- Patent' of the United states,v is:

l. A- magnetic induction accelerator comprising: a source of charged particles, means inprox'imity' to said source for projecting the particles along a desired path, electromagnetic meansin intimate inductive relation witlr said p'ath for sub jecting charged particles to an increasing mag netic flux whereby such particles are accelerated;

" and energy-supplying means? forming a" part of said electromagnetic m'eansand operative after predetermined acceleration of said particles to increasethe rate of change of" said flux; thereby to compensate for radiation 1o'sses occurringas said particles attain high energy levels.

21 Apparatus having means by which charged-' particles may be accelerated comprising'a source; of charged particles; means in proximity to said source for projecting" the particles along a de sired path, electromagnetid meansinductively coupled with said path for producing a changing. magnetic guide field for confining such particles to an orbital path in spite of increases in the energy of said particles, and electromagnetie means in intimate inductive relation with said path for producing a changing magnetic fiuX linking said path" in order to-induce acceleration of'sa'idparticles, the rate of change of' said flux being similar to the rate of change" of" the guide field over an initial period and being" greater than such rate of change over a second period in order to ofiset radiati'on losses of the acceler ateld particles;

3. Apparatus having means by which charged particles may be accelerated along an orbitaf path, electromagnetic means in intimate inane:- tive relation with said path for producing a magnetic field in the locus of said path which i-ncreases at a predetermined ratejelectromagnetlc means inductively coupled with said path for aisamro producing. magnetic 'fiux which "links said path and which varies over an. initial period at a rate similar to the rate of increase of said field, whereby said particles are maintained in said path by said field in spite of acceleration caused by said flux, andener y-supplying means forming a part of said electromagnetic means and operative to selectively increase the rate of change of said flux after said particles have'attained substantial energy, thereby to offset radiation losses tending to cause premature deviation of said particles fromsaidorbital path,

4. Apparatus in which charged particles-are to be accelerated along an orbital path, comprisingiia coil inductively.coupledttosaid path tending when energized to produce a magnetic guide field in the locus of said path and a magnetic flux linking the path, a second coil inductively coupled to said path primarily for producing a flux which centrally links said path, said coils being in bucking relation with respect to voltages induced by fiux which links the path, energysupplying means for increasing the excitation of said coils at similar rates during an initial period to accelerate charged particles along said orbital path while maintaining them in said path by the action of said guide field, and energy-supplying means for increasing the excitation of said second coil with respect to said first coil at a predetermined point in the operating cycle thereby to prevent unwanted deviation of said particles from said path because of energy losses attributable to radiation.

5. Apparatus in which charged particles are to be accelerated along an orbital path, compris- I ing: a coil in intimate inductive relation with said path and tending when energized to produce a magnetic guide field in the locus of said path and a magnetic flux linking the path, a second coil in intimate inductive relation with said path primarily for producing an accelerating fiux which centrally links said path, said coils being in bucking relation with respect -to voltages induced by flux which links the path, energy-supplying means for increasing the excitation of said coils at similar rates during an initial period to, accelerate charged particles along said orbital path while maintaining them in said path by the action of said guide field, and electronic switching means in circuit with said second coil for selectively increasing the excitation of said coil with respect to said first coil at a predetermined point in the operating cycle thereby to offset the effect of energy losses attributable to electromagnetic radiation by said particles.

6. Apparatus in which charged particles are to be accelerated along an orbital path, comprising: a coil in intimate inductive relation with said path tending when energized to produce a magnetic guide field in the locus of said path and a magnetic flux linking said path, a second coil in intimate inductive relation with said path primarily for producing an accelerating flux which links said path, saidcoils being in bucking relation with respect to voltages induced by flux q vi first and second coils and a terminal'of said source which is at a desired potential difference with respect to said first terminal, a connection be tween a point common to said second coil and said capacitor and a terminal of said source intermediate in potential between said first and second terminals, and means operative at a predeter mined time in the operating cycle to shift the connection of said second mentioned point the 3 terminal of said source having a higher potential intimate inductive relation with said path tending when energized to produce a magnetic guide field in the locus or said path and a magnetic flux linking said path, a second coil in intimate inductive relation with said path primarily for producing an accelerating flux which links said path, said coils being in bucking relation with respect to voltages induced by flux which links said path, a parallel resonant circuit including said first coil in one branch thereof and a capacitor in series with said second coil in the other branch thereof, a source of potential for exciting said resonant circuit at its proper frequency, said source having a plurality of terminals of varying potential difference, a connection between a terminal of said source and a point common to said first coil and said capacitor, a connection between the common point of said first and second coils and a terminal of said source which is at a desired potential difference with respect to said first terminai, a connection between a point common to said second coil and said capacitor and a terminal of said source intermediate in potential between said first and second terminals, and an electronic switching circuit actuable at a predetermined time in the operating cycle to shift the connection of said second mentioned point to a terminal of said source having a higher potential difference with respect to said first and third terminals than does said second terminal, whereby the flux linking said path is increased with respect to the field at the locus of the path in order to compensate for radiation losses occurring as the accelerated particles reach high energy levels.

8. Apparatus in which charged particles are to be accelerated along an orbital path, comprising: electromagnetic means inductively coupled to said path for producing in linkage with said orbital path a symmetrical alternating magnetic flux for inducing acceleration of said particles, electromagnetic means inductively coupled to said path for producing in the locus of the path an asymmetric alternating magnetic field serving to maintain said particles in said path, the rates of change of said flux and said field being initially correlated, and energy-supplying means forming a part of said electromagnetic means and operative at a predetermined point in the operating cycle to selectively increase the rate of change of said fiux to compensate for losses attributable to electromagnetic radiation as said particles attain high energy levels. r

9. In apparatus in which charged particles are to be accelerated along an orbital path, a coil in intimate inductive relation with said path and tending when energized to produce a magnetic guide field in the locus of said path and a further fiux centrally linking said path, a second coil also in intimate inductive relation with said path primarily for producing an accelerating flux 15 which links said path, said coils being in bucking relation with respect to voltages induced by flux which links the path, means for passing unidirectional current serially through said coils to produce a biasing magnetic field at the locus of said path, Without producing a corresponding flux centrally linking said path, means for sinusoidally varyin the excitation of said coils at similar rates during an initial period to accelerate said particles along, said path while maintaining them in said path by the action of said guide field, and means for selectively increasing the rate of change of excitation of said second coil with respect to said first coil at a predetermined point in the operating cycle, thereby to prevent un- 15 2,447,255

16 wanted deviation of said particles from said path because of energy losses attributable to radiation.

WILLEM F. WESTENDORP.

REFERENCES CITED The foliowlng references are of record in the 10 Number Name Date 2,139,238 Linder Dec. 6, 1938 2,297,305 Kerst- Sept. 29, 1942 2,331,788 Baldwin Oct. 12, 1943 2,394,072 Westendorp Feb. 5, 1946 Kerst et al Aug. 17, 1948 

